I am 17, and have a step-sister (Maria) who is also 17. She has an ABSOLUTELY SMOKIN body, which I had never seen naked, but often in her bras and panties, usually thongs and she had often seen me in her boxer briefs. Last summer I came home early one day, and walked upstairs to my bedroom. No one else was home. As I passed my sister's room, the door was slightly open, and Maria was lying on her bed, dressed only in a lacy white thong, no bra. One of her hands was feeling her right nipple, and the other was down the front of her thong. I stood there for a minute, totally in awe of her beautiful body (she has like perky 'B' cup breasts, and a totally flat tummy with a beautiful butt.)

I had already sprung a full-fledged erection from the brief time I had watched her, and had my hands down the front of my shorts. I cleared my throat to let her know I was there, and she stopped and looked up at me. I asked Maria what she was doing, and she said 'DUH, the same thing you guys do.....' I was pretty stupid and asked her if girls did that too. Maria looked at me with a grin and said she would show me if I was interested, since at some time I would have a girlfriend that would do it. I said that would be awesome, and to continue like I wasn't there. I sat in a chair across from her bed. Maria stripped off her thong, and said there was one condition. I asked what, and she threw her thong at me and said 'Brian......you have to wear this while I do.' I said 'NO WAY' and with that she got up and said 'have it your way' and started to put on her robe. By now I was SOOOOOO horny I would have done anything to see her finish. I finally said I would put on her thong, and she stood in front of me, in her robe,with the front open showing shaved and neatly trimmed pubes. She put her hands on her hips, and so 'Well......'

I told her I was embarrassed, and she asked me if I wanted to watch or not. So I slowly stripped off my shirt, shorts, and boxers. I picked up her thong, and slipped it on. Surprisingly, it fit pretty well, even over my erection, and it actually felt really sexy, especially when the thong slipped into my crack. Maria laid back down on the bed, and started to masturbate again. She rubbed her clit, and eventually slipped a finger in her hot pussy. I could hear the wetness in her crotch. I had too much, and started to rub myself. Maria commanded 'NO......NOT YET. ' She continued to rub herself for about another 4 minutes until she finally heaved her chest, sunk a finger deep into her pussy, and moaned she was cumming.

It took a minute, but Maria calmed down. She rolled over on her side, and grabbed my boxers. She said 'Now Brian......it's your turn......' I knew what she meant, and put my hand down the front of her thong that I now had on. As I did, she pulled on my boxer briefs . I pulled my dick and balls out, with the front of the thong under my balls, and started to jack off. Maria looked at me and said 'Well......I see my step brother shaves.......I love it when a guy shaves.........' meaning I do shave my balls cause my girlfriend likes me to. She slipped her hand in the front of my boxers, as I continued to jack slowly, (I was already very close to being there....and it was pretty strange to have your step-sister watch you jack off, but I figured since she had done herself, turnabout would be fair play.) Maria has a digital clock in her room, and it took me less than 2 minutes to shoot a huge load all over myself, and her thong. I waited to go soft, and stood up, slipped off her thong, and handed it back to her saying I was sorry I had 'jizzed' it up. Maria took if from me, and simply smiled and said..........'Maybe I'll just put it in my drawer and keep it this way Brian...... Sometimes I need a little fantasy like guys do' Maria stripped off my boxers and threw them in my face. She said 'maybe you would like a little fantasy time, too.......'